For example, when sunshine filtering through leaves is captured by a camera as illustrated in FIG. 1, a phenomenon in which highlighted regions h1 to h5 surrounded by the dotted line circles are colored with green or magenta is seen.
FIG. 2(a) illustrates a Bayer array made of RGB pixels and used in many conventional cameras.
FIG. 2(b) illustrates a RGBW array which has been increasingly used in recent cameras. Each of RGB pixels is a pixel including a filter selectively transmitting light of a wavelength region of R, G or B, and a W pixel is a pixel including a filter that transmits almost all the visible light of the RGB wavelength light.
When the image illustrated in FIG. 1, that is, the image having a high brightness region of a small area of about several pixels like the sunshine filtering through leaves is captured with the camera including an imaging device of the RGBW array including the W pixels as illustrated in FIG. 2(b), a false color such as green or magenta is generated in the highlighted regions h1 to h5 which are small high brightness regions.
Hereinafter, the false color, which occurs in the highlighted region of a small area of about several pixels, is called brightness false color.
A principle of occurrence of the brightness false color will be described with reference to FIGS. 3(a) and 3(b).
For example, as illustrated in FIG. 3(a), when the area of the highlighted region is small and the pixels of the highlighted region are configured from almost only the W and G pixels, pixel values of the G pixels are relatively larger than peripheral R and B pixels. As a result, color balance is lost, and the region is colored to green.
Further, as illustrated in FIG. 3(b), when the area of the highlighted region is small and the pixels of the highlighted region are configured from almost the W, R, and B pixels, the pixel values of the R and B pixels are relatively larger than the pixel values of the peripheral G pixels. As a result, the color balance is lost, and the region is colored to magenta.
As described above, various patterns of false colors, that is, the brightness false colors are generated, depending on the configuration of the pixels included in the highlighted region that is a high brightness portion.
To decrease such a brightness false color, processing of correcting the false color occurring region using an optical low-pass filter is effective. That is, the processing is to decrease a high-frequency component of light incident on the imaging device, and to correct extreme change of the pixel value into gentle change. However, this method causes a decrease in resolution, resulting in deterioration of image quality, and thus it cannot be said that the method is an appropriate method.
Note that, a technology to decrease the false color typically called purple fringing is described in, for example, Patent Document 1 (Japanese Patent Application Laid-Open No. 2009-124598) and Patent Document 2 (Japanese Patent Application Laid-Open No. 2006-14261).
The purple fringing is caused mainly by an aberration of a lens included in the camera, and is a false color occurring around a high contrast edge of blown-out highlight.
However, the brightness false color described above is caused in a pixel region that does not have blown-out highlights. Therefore, there are some cases which cannot be handled by the conventional processing of decreasing the purple fringing.